The present application claims priority to Japanese Application No. P11-152931 filed May 31, 1999, which application is incorporated herein by reference to the extent permitted by law.
1. Field of the Invention
This invention relates to a method for recycling a high-quality regenerated styrene resin from a waste styrene resin, such as expanded styrene or styrene cabinets, or waste styrene resin doped with a combustion-retardant agent, such as expanded styrene or styrene cabinets doped with a combustion-retardant agent.
2. Description of Related Art
The styrene resins, doped or not doped with a combustion-retardant agent, is used extensively as a cabinet material for a variety of electric equipment or as a building material. In addition, expanded styrene is used in large quantities as a variety of packaging materials.
Recently, attempts have been made to recover and re-use the waste materials, for environmental maintenance and economic merits. For example, a proposal has been made for dissolving the waste styrene material, such as expanded styrene or styrene cabinets, in an organic solvent for reducing the volume of the waste material, the resulting solution is transported to a recycling plant where it is heated in vacuum to remove volatile components to remove the organic solvent to recycle the residual product as regenerated styrene.
The above-described recycling system suffers a problem that the solvent which has dissolved the expanded styrene or styrene cabinets in the regenerated styrene be left over in the regenerated styrene. If the organic solvent is left over in the regenerated styrene, its heat resistance or tensile strength is appreciably lowered to degrade the quality of the regenerated styrene. In particular, ester-based solvents are high boiling such that the solvent is liable to be left over even on heating in vacuum for removing volatile components. If the heating temperature is raised to lower the amount of the residual solvent, the styrene resin tends to be thermally decomposed to lower the strength of the styrene material.
Moreover, a heating step is included in the recycling process, such that, if the recycling process is carried out in vacuum, oxidation is produced under the effect of residual oxygen, such that the molecular weight of the regenerated styrene resin is decreased. If the molecular weight is decreased, the regenerated materia is lowered in tensile strength and impact strength, thus appreciably lowering its quality.
On the other hand, expanded styrene doped with a combustion-retardant agent, used as a building material, or expanded styrene doped with a combustion-retardant agent, used as a cabinet for a television receiver, contains a halogen-based combustion-retardant agent in an amount approximately 1 to 10 wt %. If the styrene resin containing the combustion-retardant agent is heated to a temperature of 200xc2x0 C. or higher, the combustion-retardant agent is thermally decomposed to yield an acid which leads to significantly lowered strength of the styrene resin and hence to significantly lowered quality of the regenerated styrene. On the other hand, the processing equipment is attacked by acids yielded on thermal decomposition of the combustion-retardant agent. Thus, no effective recycling method has so far been established, such that the major portions of the waste styrene resin doped with the combustion-retardant agent are used as a land-filling material or a starting material for high-furnaces or incinerated for disposal. As the combustion-retardant agent, halogen-based combustion-retardant agents are used as a rule, so that dioxins are feared to be produced in the course of incineration for disposal.
It is therefore an object of the present invention to provide a method for disposal for effectively decreasing the amount of residual solvents in the regenerated styrene resin and for preventing oxidation of the styrene resin in the course of the recycling, and therewith a recycling method which allows for recycling of the high-quality regenerated styrene resin.
It is another object of the present invention to provide a method for disposal for effectively decreasing the residual amount of the combustion-retardant agent in the regenerated styrene resin and therewith a recycling method which allows for recycling of the high-quality regenerated styrene resin.
In one aspect, the present invention provides a method for recycling a waste styrene resin material including dissolving the waste styrene resin material in an organic solvent boiling at a temperature lower than 200xc2x0 C. and having solubility not less than 15 wt % at room temperature to prepare a solution of the waste styrene resin material, removing impurities from the solution of the waste styrene resin material; and vacuum heating the solution of the waste styrene resin material freed of the impurities to remove volatile components and the organic solvent to reduce the amount of the residual solvent in the styrene resin to not larger than 0.4 wt % to recycle the resulting styrene resin as a regenerated styrene resin.
According to the present invention, since the waste styrene resin material is dissolved in an organic solvent boiling at a temperature lower than 200xc2x0 C. and having solubility not less than 15 wt % at room temperature, the amount of the organic solvent used is diminished to improve the operating efficiency. By setting the amount of the residual solvent in the styrene resin to 4 wt % or less, characteristics of the material of the regenerated styrene resin, such as the thermal resistance or tensile strength, may be maintained at optimum values.
In another aspect, the present invention provides a method for recycling a waste styrene resin material doped with a combustion-retardant agent including dissolving the waste styrene resin material doped with the combustion-retardant agent in an organic solvent boiling at a temperature lower than 200xc2x0 C. and having solubility not less than 15 wt % at room temperature to prepare a solution of the waste styrene resin material, removing the combustion-retardant agent from the solution of the waste styrene resin material to give an amount of the residual combustion-retardant agent in the styrene resin to not larger than 1% and vacuum heating the solution of the waste styrene resin material freed of the combustion-retardant agent to remove the volatile components and the organic solvent to reduce the amount of the residual solvent in the styrene resin to not larger than 0.4 wt % to recycle the resulting styrene resin as a regenerated styrene resin.
According to the present invention, since the waste styrene resin material doped with the combustion-retardant agent is dissolved in an organic solvent boiling at a temperature lower than 200xc2x0 C. and having solubility not less than 15 wt % at room temperature, the amount of the organic solvent used is diminished to improve the operating efficiency. By setting the amount of the residual solvent in the styrene resin to 4 wt % or less, characteristics of the material of the regenerated styrene resin, such as the thermal resistance or tensile strength, may be maintained at optimum values. Moreover, by setting the amount of the residual solvent in the styrene resin to 4 wt % or less, the amount of the acid yielded on thermal decomposition of the combustion-retardant agent may be diminished to affect the strength of the material of the regenerated styrene resin only to a lesser extent to evade attacking the processing equipment.
According to the present invention, as described above, in which the waste styrene resin material is dissolved in an organic solvent boiling at a temperature lower than 200xc2x0 C. and having solubility not less than 15 wt % at room temperature, the amount of the organic solvent used may be diminished to improve the operating efficiency. By setting the amount of the residual solvent in the styrene resin, characteristics of the material of the regenerated styrene resin, such as thermal resistance or tensile strength, may be maintained at optimum values. This renders it possible to recycle the high-quality regenerated styrene resin.
Moreover, according to the present invention, as described above, in which the waste styrene resin material doped with the combustion-retardant agent is dissolved in an organic solvent boiling at a temperature lower than 200xc2x0 C. and having solubility not less than 15 wt % at room temperature, the amount of the organic solvent used may be diminished to improve the operating efficiency. By setting the amount of the residual solvent in the styrene resin to not higher than 0.4 wt %, characteristics of the material of the regenerated styrene resin, such as thermal resistance or tensile strength, may be maintained at optimum values. Moreover, by setting the amount of the residual combustion-retardant agent to not larger than 1%, the amount of the acid yielded on thermal decomposition of the combustion-retardant agent may be diminished to eliminate adverse effects of the regenerated styrene resin on the strength of the resin material or on the processing equipment.
Thus, the added value of the regenerated styrene resin doped or not doped with the combustion-retardant agent and the application may be raised to reduce the waste material to save natural resources and energy.